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OSPF selects DR to reduce the network traffic and all the traffic are send to DR. DR gets a lot of load and needs a lot of computing resource. Why does OSPF selects DR with the highest ip address ?? Does selecting like this ensures that best router is selected ?

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Let me clarify a misunderstanding: The DR is responsible for updating the LSDBs of the other routers on the network segment. It does not receive all the network traffic.

All the non-DR routers make routing decisions and forward traffic. The purpose of the DR is to reduce routing update traffic and the number of adjacencies each router needs to maintain.

The DR is elected based on the priority value in the hello field. This allows you, the administrator, to choose which router becomes the DR. If more than one router has the same priority (or you don't set it), then the highest router ID is used as a tie-breaker.

Note that while the router ID looks like an IP address (and is often written that way), it is not an IP address -- just a (unique) number.

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    Cisco uses the IP (v4) address of the first configured loopback interface (or actual interface) if you don't explicitly set it. (cisco never creates a random router ID.) Yes, in OSPF it's just a number, but everything/everybody shows it as an IP address. – Ricky Beam Jan 2 '16 at 0:39

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